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**woca****Member**- Registered: 2006-01-14
- Posts: 4

Hi all,

Some questions,

1) The speed of an electric motor rises from 1430 to 1490 rev/min in 0.5 seconds.

Find the average angualr acceleration and the number of revolutions turned through this time.

2)The speed of a shaft increases from 300 to 360 rev/min while turning through 18 complete revolutions.

Calculate the angular acceleration and the time taken for this change.

Goodluck to all those who try. Please post any answers with working. Hopefully I will also be posting some answers soon.:)

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**Ricky****Moderator**- Registered: 2005-12-04
- Posts: 3,791

Hopefully I will also be posting some answers soon.

Huh? If you think you can do the problems, try them first before asking for help. If you want us to check your answers, then post all your work. It makes it easier for us to help you.

"In the real world, this would be a problem. But in mathematics, we can just define a place where this problem doesn't exist. So we'll go ahead and do that now..."

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**woca****Member**- Registered: 2006-01-14
- Posts: 4

I am, im working on them now..., thats why I said I will be posting answers soon.

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**irspow****Member**- Registered: 2005-11-24
- Posts: 457

1) average α = Δω / Δt

α = [((1490 - 1430)rev/min) / .5s][60s/min] = 7200rev/min

(They tried to trick you using different units.)

2) Again the definition of α is the same, assuming constant acceleration. We can solve for t using their hint of how many revolutions occured during the time period.

18 revs / [(360 + 300)revs/min]/2 = 0.05454...min

or 3/55 min.

α = Δω/Δt = (360 - 300) / (3/55)

α = 1100rev/min²

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